In oil recovery, storage and transportation operations, hydrocarbon gases are produced from oil condensate storage tanks and other sources through flash losses, working losses, standing losses, and breathing losses, where liquid hydrocarbons evaporate into gaseous form. Working losses occur when the liquids are agitated, i.e., when new liquids are pumped into the tanks; breathing losses are primarily the result of diurnal heating of the tanks; and flash losses occur when liquid hydrocarbons experience a sudden pressure drop, an example of which can occur when liquid hydrocarbons move from a separator (i.e., at approximately 30-400 psig or more) to an oil condensate storage tank at much lower pressure (i.e., 0 to 2 psig). Flash losses account for a significant portion of total losses. Collectively, all of these losses of hydrocarbon gases are referred to herein interchangeably as “flash emissions,” “vent gas,” “flash gas,” “vapor” and combinations thereof. As recognized by the present inventors, all of these losses may occur in a variety of situations involving oil storage tanks, vapor recovery towers, three-phase separators, water storage tanks (for instance as used in oil and natural gas production operations), flow-back tanks (for instance as used in hydraulic fracturing operations), and during the transportation of oil and gases with rail cars, oil hauling trucks, offloading stations and the like.
Flash emissions include Volatile Organic Compounds (VOC) and therefore pose a hazard to air quality as they form ground level ozone when they react with NOx. Historically, such gases were vented through relief valves of the storage tanks into the atmosphere.
To protect the environment and the health of the public at large, the permissible levels for ground level ozone and, in turn, uncontrolled flash emissions from flash gas sources such as oil storage tanks are regulated by various regulatory agencies at federal and state levels. Methods of flash emissions control include flaring, where the flash emissions are burned off, and more advanced systems of vapor recovery that capture, compress, and inject these flash emissions into nearby gas gathering pipelines, such as described in U.S. Pat. No. 7,350,581.